The present invention relates to fluid piping systems and more particularly to piping systems of the type wherein a metallic housing is lined with a non-metallic material selected from the group consisting of elastomers and plastomers.
Lined piping systems of the foregoing type that are presently in use are generally fabricated from Schedule 40 or Schedule 80 steel and lined with various chemically resistant plastics having nominal wall thicknesses usually ranging from about 0.054" for 1/2" pipe to about 0.185" for a 12" pipe for TFE resin, and thicker for other resins such as heavy duty polypropylene. Occasionally, Schedule 10 steel has been used. Generally, connections are made between sections of such pipe by flange joints, in which case the lining is brought out of the pipe and flared over the face of the flange both to protect the metal from the fluids being carried and to serve as a gasket. The flanges have been predominantly of the bolted kind, and at one time it was considered desirable to include a fibrous backup washer around the liner between the metal flange face and the overlying plastic flare to compensate for cold flow of the plastic.
The known piping is quite heavy, and bolting up standard flanges requires considerable man hours to effect a typical installation. However, there has been a general reluctance in the market place to trust joints other than bolted flanges. Nevertheless, there is a need, particularly in the light of rising costs of capital improvements, for a lighter weight, more quickly assembleable, plastic lined piping system.
An attempt in this direction is represented by the pipe assembly disclosed in U.S. Pat. No. 4,313,625 issued Feb. 2, 1982. The abstract of said patent refers to a lined pipe assembly wherein the lined pipe and liner are deformed to provide an outwardly flaring flange, a loose tapered ring is disposed on the pipe adjacent the flange and the pipe is joined to a similar pipe or cast fitting by means of a split "V" clamp. However, loose rings are the bane of the workman. If they are made sufficiently snug to restrict travel along the pipe there is the risk that they will hang up on the pipe when the joint is assembled preventing the development of a uniformly sealed joint. Therefore, a certain looseness is required and it becomes a problem to hold the rings in place until the "V" clamp can be installed.
There are additional drawbacks to the construction disclosed in said patent and these will be mentioned below when describing the present invention.